diff --git a/src/upgrades/1.15.0/fullname_search_set.js b/src/upgrades/1.15.0/fullname_search_set.js
index 9f479af145..c3955226bd 100644
--- a/src/upgrades/1.15.0/fullname_search_set.js
+++ b/src/upgrades/1.15.0/fullname_search_set.js
@@ -16,7 +16,7 @@ module.exports = {
 			const userData = await user.getUsersFields(uids, ['uid', 'fullname']);
 			const bulkAdd = userData
 				.filter(u => u.uid && u.fullname)
-				.map(u => ['fullname:sorted', 0, u.fullname.substr(0, 255).toLowerCase() + ':' + u.uid]);
+				.map(u => ['fullname:sorted', 0, String(u.fullname).substr(0, 255).toLowerCase() + ':' + u.uid]);
 			await db.sortedSetAddBulk(bulkAdd);
 		}, {
 			batch: 500,